The invention relates to metal clad articles, and more particularly to fiber-reinforced plastic tanks with metal liners.
Compressed or pressurized gases are typically contained in a generally cylindrical tank. The tank ends are generally rounded and one of the ends is sealed while the other of the ends forms an outlet or connecting stud through which the gas can enter or exit the tank. The tank is typically formed from steel. It is also known in the art to provide a metal liner adjacent the inner surface of a a fiber-reinforced plastic tank to seal the tank against loss of the gas from the tank. Without a metal liner, the pressurized gas can diffuse through the fiber-reinforced plastic shell. Since steel is four times as heavy as fiber-reinforced plastic, it is desirable to use more fiber-reinforced plastic than steel.
It is also known in the art to provide an aircraft fuel tank with a linearly corrugated metal liner as shown in U.S. Pat. No. 2,144,945. The corrugated metal liner provides support to the shell of the tank. It is also known in the art to provide a resin layer between the tank and the liner, as shown in U.S. Pat. No. 4,421,827.
Typically, the material forming the metal liner has a high modulus of elasticity relative to the modulus of elasticity of the fiber-reinforced plastic shell (greater than four times). Thus, the liner is much more stiff than the fiber-reinforced plastic shell. If a force is applied to the shell, as for example, when the tank is accidently dropped, the shell may elongate more than the liner can elongate without rupturing. In order to prevent rupturing of the liner, a corrugation can be used so that the liner elongates with the shell with a movement like an accordion bellows.
However, known corrugations repeat in only one lengthwise direction, thus leaving a continuous or unbroken grid of material in the widthwise direction which cannot elongate in accordion-type fashion. Therefore, when the structure supporting the liner is loaded, the liner material can rupture in tension or buckle in compression along the unbroken linear portions of the liner and before the fiber-reinforced plastic shell is utilized to its yield strength or ultimate strength. To overcome this problem, a thick (about one fourth inch) liner is used, resulting in a much heavier tank.